I'd like to know if calling with a wireless phone at home can be heard by neighbours and if it is safe.
It depends on what you mean by "wireless phone at home":
GSM phone - then yes, all transmission between your phone and GSM station is encrypted
DECT phone - then partially: all wireless transmission between the phone and its base station is encrypted, however neighbours can plug into your analogue, unencrypted phone cable
cheap no-name wireless phone - it depends on what technology have been used, but still your neighbours can plug to your analogue, unencrypted phone cable
You can avoid plugging to an analogue phone cable by using ISDN phone (where available), or VoiP.